1. Field of the Invention
The present invention generally relates to a technique for interaction between a scheduler and a power controller for joint scheduling and power control in a wireless communication system. More particularly, the present invention relates to a technique for joint scheduling and power control among a Base Station (BS) and Relay Stations (RSs) in order to increase fairness and transmission efficiency on a downlink in a multi-channel Distributed Antenna System (DAS) using frequency reuse and common power control.
2. Description of the Related Art
In a conventional cellular system, a scheduler selects packets to be transmitted to Mobile Stations (MSs) according to their priority levels. MSs suffer from different amounts of signal attenuation, frequency selectivity, and interference according to their respective locations at any given time. If the MSs are allocated the same amount of transmit power, they will typically have different Signal-to-Interference and Noise Ratios (SINRs). To make the SINRs of the MSs uniform, a power controller allocates higher power to remote MSs and lower power to nearby MSs.
In a multi-channel DAS using a frequency reuse and common power control protocols, the link between a BS and an RS is established by a dedicated line, such as an optical fiber, and each RS functions like the BS, that is, RSs serve as distributed antennas of the BS. The BS and the RSs have their independent service areas, and frequencies can be reused in the service areas. It may occur that two MSs are located next to the boundary between the service areas, although in the different service areas and sharing the same channel. When a scheduler selects packets for the MSs, the MSs have low SINRs due to interference from the neighboring service areas and thus the transmission of the packets to the MSs is highly probable to result in failure. If higher power is allocated to the MSs to increase their SINRs, the resulting increased mutual interference continues to nullify the effect of the power control. If a subchannel with a low fading gain is allocated to an MS in a multi-channel system, the resulting large signal attenuation leads to much power consumption in order to achieve a target SINR. The increased power interferes with other MSs, thereby decreasing the SINRs of these MSs as well. This interference is a result of power control and channel allocation being performed after scheduling. As scheduling, power control, and channel allocation all take place independently, data transmission to MSs will often fail, or a minimum data rate is not met, thereby causing an outage. Accordingly, there has been a long-felt need in the art to address the aforementioned problems.